Correlation between the stoichiometry and the bistability of electronic states in valence-tautomeric RbxMn[Fe(CN)6]y•zH2O complexes

A series of Prussian blue analogues, RbxMn[Fe(CN)6]y center dot zH(2)O with different stoichiometries have been synthesized. Elemental analyses reveal a quasilinear decrease in x and y when z increases. Some of these samples present a first-order phase transition between the Mn-II-Fe-III and Mn-III-Fe-II electronic states with large thermal hysteresis loops observed in the magnetic susceptibility. The phase-transition temperatures correlate with the stoichiometry, but quantitative predictions cannot be made because of the disordered nature of the compounds. Contrary to previous literature reports, calorimetric and Raman spectroscopic measurements reveal that the charge-transfer phase transition is accompanied by a significant entropy change, Delta S = 48-59 JK(-1) mol(-1), of mainly vibrational origin. In addition to the thermal phase transition, Raman spectra also show that below ca. 120 K a photoinduced Mn-III-Fe-II to Mn-II-Fe-III. conversion occurs in certain stoichiometries. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007.